1. Field of the Invention
The present invention relates to a device for cutting threads formed on a sewing machine and, more particularly, to a device for cutting, in a scissor-like action, a serging chain comprised of two or more threads.
2. Description of the Prior Art
The prior art discloses a wide variety of devices that are used in combination with sewing machines to cut or sever threads. For example, in U.S. Pat. No. 2,423,001, issued to Blowers, a series of enchained thread loops are severed by means of a sharp cutting blade. Still further, U.S. Pat. No. 2,508,236, issued to Enos, discloses a thread-severing and nipping member of thin spring steel. Both of these references disclose devices for severing thread. A problem associated with these prior art devices, is that the threads are broken by pulling them under tension across a severing, or cutting, edge which frequently results in a poor cut. As the thread cutting, or severing, device gets dull and loses its sharp edge, the incidence of poor cuts increase. In addition, as multiple threads are cut, as in the instance of three-thread chains used for a serge seam, a smooth, more precise cut is required. This type of cut is often difficult to obtain by severing the threads.
A multi-thread chain of three, four or five threads is normally used on the assembly of fabric on an overlock sewing machine. These chains are typically 1/8th to 1/4th inch in diameter and are cut with a pull back knife normally supplied by the sewing machine manufacturer. It has been found to be tedious and difficult to make a smooth cut with this type of severing device. To sever the chain requires pulling the chain under tension across the cutting edge of the pull back knife. Too little thread control tension results in a flat sewn seam but having inconsistent quality. Too much thread control tension results in a puckered seam, but having a satisfactory out.
Various electro-mechanical devices, electric clippers and impact cutters can produce smooth and uniform cuts. These devices are expensive to purchase and maintain. Thus, there is a need for an inexpensive chain cutting device that yields consistent and uniform thread chains.